The present invention relates to colored electrochromic transparent window assemblies. More particularly, the present invention relates to transparent window assemblies incorporating desired coloring characteristics based on electrochromic principles, particularly useful in motor vehicles and buildings.
Electrochromic devices have been proposed for a number of uses, such as architectural windows and automotive windows and mirrors. Such electrochromic devices typically include a sealed chamber defined by two pieces of glass that are separated by a gap or space that contains an electrochromic medium. The glass substrates typically include transparent conductive layers coated on facing surfaces of the glass and in contact with the electrochromic medium. The conductive layers on both glass substrates are connected to electronic circuitry that is effective to electrically energize the electrochromic medium to change the light transmission through the medium. For example, when the electrochromic medium is energized, it can darken and begin to absorb light, which can involve a color change of the medium.
Electrochromic devices have most commonly been used in rear-view mirrors for automotive applications. In such uses, a photocell can be incorporated into the electrochromic cell to detect a change in light reflected by the mirror. When a specific level of light is reflected, for instance when lights are reflected at night, the photocell can activate to apply an electrical potential to the electrodes in the cell, thus causing the electrochemical medium to change color and create a darkening affect, thereby dimming the mirror to the lights. Electrochromic devices have also been mentioned for use in other automotive applications, such as windows and sunroofs, as well as architectural applications such as building windows.
The color of windows can provide certain aesthetic considerations, particularly in automobiles and architectural applications. For instance, specific glass colors are chosen to coordinate with the color of the paint of an automobile or the surrounding environment.
The perceived color of an object, and in particular glass, is highly subjective. Observed color will depend on the lighting conditions and the preferences of the observer. In order to evaluate color on a quantitative basis, several color order systems have been developed. One such method of specifying color adopted by the International Commission on Illumination (CIE) uses a dominant wavelength (DW) and excitation purity (Pe). The numerical values of these two specifications for a given color can be determined by calculating the color coordinates x and y from the so-called tristimulus values X, Y, Z of that color. The color coordinates are then plotted on a 1931 CIE chromaticity diagram and numerically compared with the coordinates of CIE standard illuminant C, as identified in CIE publication No. 15.2. This comparison provides a color space position on the diagram to ascertain the excitation purity and dominant wavelength of the glass color.
In another color order system, the color is specified in terms of hue and lightness. This system is commonly referred to as the CIELAB color system. Hue distinguishes colors such as red, yellow, green and blue. Lightness, or value, distinguishes the degree of lightness or darkness. The numerical values of these characteristics, which are identified as L*, a* and b*, are calculated from the tristimulus values (X, Y, Z). L* indicates the lightness or darkness of the color and represents the lightness plane on which the color resides. a* indicates the position of the color on a red (+a*) green (xe2x88x92a*) axis. b* indicates the color position on a yellow (+b*) blue (xe2x88x92b*) axis. When the rectangular coordinates of the CIELAB system are converted into cylindrical polar coordinates, the resulting color system is known as the CIELCH color system which specifies color in terms of lightness (L*) and hue angle (Hxc2x0) and chroma (C*). L* indicates the lightness or darkness of the color as in the CIELAB system. Chroma, or saturation or intensity, distinguishes color intensity or clarity (i.e. vividness or dullness) and is the vector distance from the center of the color space to the measured color. The lower the chroma of the color, i.e. the less its intensity, the closer the color is to being a so-called neutral color. With respect to the CIELAB system, C*=(a*2+b*2)1/2. Hue angle distinguishes colors such as red, yellow, green and blue and is a measure of the angle of the vector extending from the a*, b* coordinates through the center of the CIELCH color space measured counterclockwise from the red (+a*) axis. As used herein, Hxc2x0 will be expressed as a value between 0xc2x0-360xc2x0. The CIELAB system is superimposed over the CIELCH system in FIG. 1 of U.S. Pat. No. 5,792,559, hereby incorporated herein which illustrates the relationship between the two systems.
It should be appreciated that the color can be characterized in any of these color systems and one skilled in the art can calculate equivalent DW and Pe values; L*, a*, b* values; and L*, C*, Hxc2x0 values from the transmittance curves of the viewed glass or composite transparency.
Typical commercial soda-lime-silica glass includes the following materials: 66-75 wt. % SiO2, 10-20 wt. % Na2O, 5-15 wt. % CaO, 0-5 wt. % MgO, 0-5 wt. % Al2O3, 0-5 wt. % K2O, 0-1 wt. % BaO. To this base glass, varieties of colorants are added to produce a desired glass color. As used herein, a glass is considered to be a colored glass if its luminous transmittance (as is discussed later in more detail) is xe2x89xa687%, irrespective of total glass thickness. Glass having a luminous transmittance of  greater than 87% is considered to be clear. It should be appreciated that when a xe2x80x9cglassxe2x80x9d or xe2x80x9cglass substratexe2x80x9d is referred to herein as colored, in the case of a composite transparency having two or more glass plies, the combined thickness of all the plies is determinative as to whether the glass or glass substrate of the transparency is colored.
Many of these colored glasses, which are well known in the art, are used in automotive and architectural applications and absorb more solar energy than clear soda-lime-silica glass. The primary colorant in typical green tinted glasses used in automotive applications is iron, which is present in both the Fe2O3 and FeO forms. Other glasses include additional colorants such as cobalt, selenium, nickel and/or chrome to produce blue, bronze and gray colored glasses, as is known in the art. As known in the prior art, colorants can also be added to the basic iron containing soda-lime-silica glass composition to reduce the color intensity in the glass, and in particular to produce a neutral gray glass as described in U.S. Pat. No. 5,792,559 hereby incorporated by reference. Combinations of colorants, e.g. combinations of cobalt and selenium, can be preferentially added to the base glass composition to produce a gray colored glass. However, addition of multiple colorants requires a reduction in iron content in order to maintain a constant visible transmittance. Since these additional colorants are less powerful than FeO in absorbing solar energy, TSET will increase and the performance ratio will decrease for the glasses which include iron, cobalt and selenium (trend line 4) as colorants. The aforementioned 5,792,559 patent also shows that it is known that colored interlayer material can be combined with glass plies to produce a desired color.
One way of comparing the performance of various solar energy absorbing glasses is to compare the ratio of luminous transmittance to the total solar energy transmittance. Luminous transmittance, LT, is a measure of the total amount of visible light transmitted through the glass. Total solar energy transmittance, TSET, is a measure of the total amount of solar energy transmitted directly through the glass. This latter property is important because most of this transmitted energy is converted to heat after being absorbed by objects on the other side of the glass. In particular, as it applies to automotive uses, heat build-up and temperature within the vehicle are directly related to TSET. This can result in uncomfortable conditions for vehicle occupants and may require an increase in the cooling capacity of an air conditioning system. In addition, it has been shown that the heat buildup accelerates material degradation within the vehicle. As used herein, this ratio of luminous transmittance to total solar energy transmittance is referred to as the xe2x80x9cperformance ratioxe2x80x9d (PR).
Unless otherwise noted, luminous transmittance data provided in this disclosure is measured for CIE standard illuminant A (LTA) and the color data (i.e. L*, a* and b*) is measured for CIE standard illuminant D65. This data is further based on a 2xc2x0 observer over the wavelength range 380-780 nanometers (xe2x80x9cnmxe2x80x9d) at 10 nm intervals in accordance with ASTM 308E-90. The dominant wavelength data is measured for CIE standard illuminant C and a 2xc2x0 observer over the wavelength range 380-780 nm using the techniques disclosed in the National Bureau of Standards Special Publication 545xe2x80x94Contributions to Color Science (see Judd, D. B., xe2x80x9cThe 1931 I.C.I. Standard Observer and Coordinate System for Colorimetryxe2x80x9d, Journal of the Optical Society of America, vol. 23, October 1933, pages 359-374). The total solar energy transmittance data provided in this disclosure to calculate the performance ratio of a glass or composite transparency is based on Parry Moon air mass 2.0 solar data and is computed based on measured transmittance from 300-2000 nm. Typical performance ratios of glasses using various colorants are illustrated in FIG. 2 of U.S. Pat. No. 5,792,559, hereby incorporated herein.
Also, it is known to combine various color dyes in electrochromic medium with clear glass substrates in such electrochromic devices in order to obtain a desired color. For example, U.S. Pat. Nos. 6,020,987 to Baumann et al. and 5,998,617 to Srinivasa et al. incorporate three separate electroactive materials as an electrochromic medium to obtain a desired color, such as a neutral gray, throughout the voltage ranges of the device.
U.S. Pat. No. 5,808,778 discloses rear view mirrors using electrochromic compounds which transmit light in the orange/red visible spectrum and which absorb light in the blue/green visible spectrum. As such, glare from high intensity halogen headlights can be reduced. Further, U.S. Pat. No. 5,239,406 discloses electrochromic devices such as rear-view mirrors and window glazings which include glass of various colors. Such electrochromic devices, however, fail to address the association between the color of the glass and the color and intensity of the dye used in the electrochromic device.
Thus, there is a need for transparent assemblies that can be made in a variety of colors and shades, which are easy to fabricate, and which can be switchable with respect to luminous transmittance.
The present invention is directed to an electrochromic transparency such as an electrochromic window assembly comprising: first and second spaced transparent substrates defining a chamber therebetween, at least one of the first and second transparent substrates having a color; and an electrochromic medium contained in the chamber, the electrochromic medium including at least one dye defining a color in an electrochemically activated state upon application of electrical potential selected from colors that coordinate with the color of one of the first and second transparent substrates and colors that complement the color of one of the first and second transparent substrates. In one nonlimiting embodiment of the invention, the window assembly is selected from automotive windshields, automotive side windows, automotive sunroofs, architectural glazings, architectural windows, architectural skylights, and aircraft transparencies and portions thereof.